The year is 407AD. Britannia, northernmost province of the divided Empire of Rome, faces collapse.
In absence of the garrison stationed in the North and West of the island have been withdrawn to face Alaric, barbarian tribes from Hibernia, Caledonia and the North remain uncontested. In the South, Saxons raid the grand villas of the Roman elite, once enriched by the trade from the islands great metropolis’s: Londinium [London], Camuledunum [Colchester] and Eboracum [York]. Roman money minting has halted in its entirety.
In Gaul, large tribes of Vandals, Burgundians, Alans, and Sueves crossed the Rhenus [Rhine], overwhelming Roman defences and threatening the collapse of the Empire. The provinces of Britannia, facing separation from the mainland, revolt. Desperate for a sense of security, the Roman armies stationed in Prima elected a common soldier of significant ability for leader named after the famed fourth century emperor, Constantine.
Constantine the Great had arisen by military coup originating in Britain in 306AD. To follow his footsteps, Constantine III would cross to the continent with the remaining army of less than 125,000 men and their families, including dependents.
[POD] The crossing was a disaster.
The Roman forces met at Portus Dubrae [Dover]. Only half of the Roman army would follow Constantine out of port. The ships didn’t make it halfway before a terrible storm diverted their course. The leader found himself washed ashore at a farm near Anderida [near Folkestone]. The 30,000-remaining led by Iustinianus and Nebiogastes, appointed magistri militum by the would-be usurper, would begin to enact strict discipline for his army while Constanine lay recovering. His recovery would be slow, and his wake would be greeted with betrayal. Nebiogastes had seized control of a small army after murdering his wife and his son, Constans (whom Constantine had placed in charge of Britannia) and departed west with 15,000 men who had declared him emperor.
Constantine led his remaining army west, following the traitor to Venta Belgarum [Winchester]. The Battle would be a short and bloody victory for Constantine, who had surrounded Nebiogastes with the promise that any traitorous soldier would be allowed to re-join his ranks to be spared if they chose to fight for him. Constantine established himself in Londinium, a city of 60,000, with no where near enough men to pose a threat to the boy Honorius on the throne in Italia, but safe in the knowledge that, for now, he would not be pursued by legion while the emperor faced annihilation by Alaric’s Visigoths.
Constantine would rebuild and reorganise his army until early 408, controlling land in south of the Empires former frontier. In the North East, a Roman army matching the size of that loyal to him under the rule of a former aristocrat, Julius. Constantine knew he had to act to unite the Roman armies and usurp Honorious. Before his nomination, he and his fellow troops had killed their leaders for failing to act against the barbarian crossing of the Rhenus into the Empire.
Iustinianus knew that Julius would retreat to the natural marshlands in the north once the base of his rebellion, Camulodunon, fell to Constantine. Combatting this, he led a division of 2,000 men to secure the marshes. Half of those would march north and join a smaller division of soldiers in Maxima Caesariensis [Yorkshire] and prevent a revolt from the Brigantes.
Constantine led an army towards Camulodunon and took the city without much resistance. Julius retreated north and met Iustinianus’ division and were slaughtered at the Battle of Camboricum. Constantine had established control over the south of Britannia.
Yet the would-be usurper would not yet cross the Oceanus Britannicus [English Channel]. News soon reaches the leader in Londinium, Saxons have seized the opportunity arisen by the chaos of Britannia, invading the undefended shores of Metaris Aest [the Wash] and pushing south. The Roman garrison at Durobrivae [Castor] is defeated, leaving few towns in defence of Londinium.
As a last act to retain power, in 411 Constantine calls for magistrates to surrender wealth to him or have it lost to an overwhelming Saxon force. With this, combined with conscription for those within the city, creates enough resistance to drive Saxons north. Constantine declares the construction of forts along the undefended shores. With lack of men to invade Gaul, this act signals the leaders decision to consolidate power on the island, to retain the Roman culture of the territory still in his possession.
By 412, the Roman Empire had lost Hispania and much of Gaul. Honorius remained on the throne. Constantine is in control of 10,000 British and Roman soldiers. While chaos in the northern regions of Britannia remains, for the time being, the relative stability of the south creates no appetite for a return to the chaotic continent.